The present invention relates to a method of producing a flat container that has a large wall thickness in the mouth and shoulder portions and a small wall thickness in the body and has a large area of flatness.
It is fairly difficult to produce containers, in particular flat ones, having a large wall thickness in the mouth and shoulder portions and, a small wall thickness in the body and none of the methods presently available are completely satisfactory. Such containers are currently produced by the following methods:
(1) a method using a flat parison in combination with a parison controller;
(2) a method using a lateral expander (Japanese Patent Public Disclosure No. 61-134224); and
(3) a sheet blowing technique.
These methods, however, have their own problems. The first method produces a flat mouth portion and incurs difficulty in providing a uniform wall-thickness distribution in the body. The second method involves difficulty in achieving a uniform wall-thickness distribution in the body. The third method presents difficulty in attaining a uniform wall-thickness distribution in the mouth portion.